Field of the Invention
The present invention relates to a fixing apparatus to be mounted in an electrophotographic image forming apparatus.
Description of the Related Art
Hitherto, in electrophotographic image forming apparatus such as a printer, a copying machine, and a facsimile machine, toner images are formed on recording materials by an electrostatic image forming unit, and then the recording materials are heated and pressurized by a fixing apparatus, to thereby melt and fix the toner images onto the recording materials. In recent years, there has been proposed and put into the market a film heating fixing apparatus as disclosed, for example, in Japanese Patent Application Laid-Open No. 2009-93141, which includes a halogen heater serving as a heater unit thereof so that a film member (fixing film) is heated with the radiation heat of the halogen heater.
In the fixing apparatus disclosed in Japanese Patent Application Laid-Open No. 2009-93141, in a fixing nip portion-forming region of the fixing film, an inner surface of the film can be heated with the radiation heat of the halogen heater. In addition, also on a side opposite to the fixing nip portion (counter-fixing nip side), radiant light can be emitted onto the inner surface of the film. In other words, the temperature in a region on the counter-fixing nip side of the fixing film is raised in advance before the region comes to the fixing nip portion. This configuration is expected to shorten the time period required to raise the temperature of the fixing film.
In the configuration of the related art described above, from a viewpoint of allowing the emission of the radiant light, it is preferred that a shielding object not be interposed between the heater and the fixing film in the region on the counter-fixing nip side if possible. However, in such a configuration, when the fixing film is deformed for some reason, the inner surface of the fixing film and the heater may come into contact with each other. As a result, various kinds of trouble may occur.
Specifically, there has been known a phenomenon in which a leading edge of the recording material that has rolled around the fixing film is caught, for example, in a thermistor in the fixing unit, and is deformed into a zigzag shape (accordion jam). When conditions to cause the fixing film and the leading edge portion of the recording material to be more forcefully pressed against each other are met, specifically, when the toner images have been formed without a margin at the leading edge portion at a time point when the recording material enters the fixing nip portion, the recording material is conveyed while rolling around the fixing film. As a result, an accordion jam occurs. When an accordion jam occurs, an outer surface of the fixing film may be pushed by the creased recording material, with the result that the inner surface thereof may be deformed to come into contact with the heater. In many cases, lubricating grease is applied to the inner surface of the fixing film. Thus, when the fixing film comes into contact with the heater, a surface of the heater may be fouled with the grease or impurities. Further, when a significant external force is applied to the fixing film, the heater may even be damaged.
In addition, a problem called an edge portion temperature rises is known, i.e., regions at both edge portions of the fixing film are locally and excessively heated in a width direction of the recording material when the size (width) of the recording material is smaller than the temperature raised regions of the fixing film at the time of, for example, fixing the toner images on small size sheets. As in fixing apparatus of other types, effective measures against this problem have still been investigated in the film heating fixing apparatus of the halogen-heater type.